The classic small-block Chevy engine is one of Detroit's all-time great powerplants. It would be safe to say that SBCs have won more races than any other engine. But by the early '90s, a seriously updated engine was needed. Work began on the GEN III in 1993, just after the GEN II "LT1" was introduced. The GEN III was to be all-aluminum, lighter, and stronger than its predecessor. By the winter of 1993, cast-iron versions of the GEN III were being tortured on test dynos and all-aluminum GEM IIIs field tested in 1995.
Test cars were thrashed in the 112-degree heat of Death Valley and 40-below temps in Canada. Prototype engines were typically run for 50 hours straight at full rpm. GEN III project chief engineer Ed Koerner even tested two GEN IIIs for 260 hours and one GEN III for 520 hours at full-throttle! Needless to say, the GEN III/LS1 was not only powerful, but also very durable. This kind of extensive testing played a major roll in the success of the C5-R and C6.R endurance racing Corvettes.
The automotive press was lusting for the C5 to have a small-displacement V-6 with double-overhead cams and one or two turbos. But these were not the parameters of C5 Corvette chief engineer Dave Hill. Commenting on the all-new LS1, Hill said, "The new LS1 has the simplicity and compactiveness of the pushrod layout, but with porting so efficient and valvetrain so light and still, it breaths like an over-head cam motor." LS1 project manager John Juriga put it this way, "Porsche performance, at a Chevrolet price."
When designing a high-performance engine, everything has to work together and engineered to the max. But two systems were serious advances—the all-aluminum block and the LS1's unique ignition system. Most of the classic SBC engines used two-bolt mains. But thanks to the new deep-skirt block, designers were able to use four-bolt mains, plus two additional bolts to the bearing cap sides. Every boss area was beefed up and internal and external ribs were built in for additional strength. The completed block weighed 107 pounds—88 pounds less than the previous SBC block.
The new heads were similar in basic architecture but radically different from the classic design, mainly in the port configuration. The new "cathedral" ports were tall and narrow to allow the injectors to be pointed to the perfect place on the intake valve. Also, each port was exactly the same to completely even out the flow. And for the first time since 1955, the firing order was changed from 1-8-4-3-6-5-7-2 to 1-8-7-2-6-5-4-3 to improve main bearing operation, reduce the stress on the crank arms, and reduce vibration.
Corvette engines started using plastic engine covers on the '92 LT1 that covered the fuel rails and sides of the intake manifold plenum. The new LS1 featured larger covers that hid the radical distributorless ignition. Rather than a single distributor and ignition coil, each cylinder had its own coil to provide more precise spark along a much shorter connecting wire to the spark plugs, with a 50-percent increase in ignition energy. Hiding under the engine cover was a new composite intake manifold that is lighter than aluminum and insulated the intake charge. A separate valley cover under the manifold did a better job of sealing the top of the engine.
The oil system was vastly improved by relocating the oil pump to the front of the engine, driven off the camshaft. This shortened the block assembly by 1 inch, allowing for a shallower oil pan, thus creating a smaller engine package. Other improvements included extensive single-plane sealing surfaces and gaskets made from a silicon-aluminum composite. The cast-iron exhaust manifolds were header-like and had bolt-on heat shields to keep under-the-hood temps as low as possible.
While on paper the LS1 only had a modest bump in power—345 hp compared to 330 hp for the '96 LT4, with torque up to 350 lb-ft from 340 lb-ft, it was more about the overall package. While the classic SBC had been developed to the max, the new LS1 was just the beginning. The LS1 evolved into the LS6 for the '01-'04 Z06, the LS2 for the '05-'07 C6 Corvette, then the 427 LS7 brute for the '06-'13 Z06, the LS3 for the '08-'13 Corvette, and the 638hp LS9 for the '09-'13 ZR1. The LS1 GEN III engine, combined with the transaxle drivetrain made the C5 the most radical advancement in Corvette history.